A 23-year-old woman with pernicious anemia, previously treated with folic acid, demonstrated an unusually rapid and severe course of neurologic deterioration. She was first seen with coma, myelopathy, and peripheral neuropathy. Her EEG showed repetitive nonperiodic suppression bursts, probably related to the severe impairment of consciousness. A sural nerve biopsy specimen revealed prominent axonal degeneration. With cyanocobalamin treatment, she regained normal mentation and the use of the upper limbs. She remains paraplegic, however, with a T10 sensory level.